1. Field of the Invention
The present invention relates to live roller conveyors having a unique assembly of padding carried on a chain adapted to drive the conveyor rollers.
2. Description of the Prior Art
Well known arrangements for transporting articles on a roller conveyor have been provided with rope type means for driving the article supporting rollers. Examples of such arrangements are seen in Hohl U.S. Pat. No. 3,040,872 of Jun. 26, 1962, Vogt U.S. Pat. No. 3,158,252 of Nov. 24, 1964, Sullivan U.S. Pat. No. 3,176,828 of Apr.26, 1965, Fleischauer U.S. Pat. No. 3,621,982 of Nov. 23, 1971, Werntz U.S. Pat. No. 4,117,923 of Oct. 3, 1978, Thwaites et al U.S. Pat. No. 4,273,239 of Jun. 16, 1981 and Turnbough U.S. Pat. No. 4,319,675 of Mar. 16, 1982.
In these examples of the prior art, the orientation of the drive rope followed conventional practice, that is, the rollers have horizontal axes and the drive rope is movable in a vertical plane. In the examples where the article supporting rollers are driven by direct-contact with rope or other friction means, the support of such means has presented problems to obtain uniform contact with a span of rollers.
Variations from rope drives for roller conveyors are exhibited in patents issued to Fogg U.S. Pat. No. 3,306,430 of Feb. 28, 1967, Bodewes U.S. Pat. No. 4,074,805 of Feb. 21, 1978, Turnbough et al U.S. Pat. No. 4,392,568 of Jul. 12, 1983, Bowman et al U.S. Pat. No. 4,441,607 of Apr. 10, 1984, White et al U.S. Pat. No. 4,458,809 of Jul. 10, 1984, and Abell U.S. Pat. No. 4,588,073 of May 13, 1986.
There are other problems presented by the foregoing prior art examples. In the rope drive the support of the rope is very important, and obtaining uniform contact is difficult when long stretches of conveyor runs are required. Then again, the rope stretch that occurs over time adds to the problem of maintaining contact. In the examples where roller chains are used to support friction pads or strips, the problems that are encountered related to the contact between the axles for the rollers in the chain and the pads so that the teeth of the chain drive sprocket do not interfere with the manner of attaching the pads. The foregoing are some of the problems which become evident upon inspection of the prior art disclosures.
In the above examples of prior art, some problems have arisen, especially with the use of the elastomer material commonly chosen for the high friction pad which will distort when the series of holes in the pad to receive the roller axles does not exactly match the distance between the protruding axles in the drive chain. The dissimilar distance can be a result of inaccurate manufacturing processes or a result of fluctuating temperature. There is a large difference in the way the elastomer pad changes dimensionally with temperature changes when compared to dimensional changes in the metal used in the drive chain over the same temperature change. The dissimilar distance causes a build up of internal stresses in the elastomer pad. The result of internal stress can range from pad distortion up to material failure. Pad distortion can cause a wavy pattern along the length of pad and that, in turn can cause unwanted side loading on the chain guide track. Pad distortion can also cause a wavy pattern along the top surface of the pad which contacts the bottom of the rollers causing excess noise and vibration.
The problem associated with the Abell patent U.S. Pat. No. 4,588,073 drive is that the chain supported pads are difficult to maintain uniform roller contact due to thermal conditions which the conveyors encounter or are intended to be subjected to, as well as the effect such thermal conditions have on the conveyor assembly.